1. Field of the Invention
The present invention relates generally to systems and methods for recording information on optical and electromagnetic recording disks. In particular, the invention relates to the use of a control disk for providing formatting and speed control information during recording on a blank recordable disk. Optionally, the control disk may also provide operating, diagnostic, and a wide variety of other information for the system or user.
2. Description of the Background Art
Optical data storage media in the form of compact disks are well known as an alternative to long playing records and magnetic tape cassettes. The disks with which consumers are familiar are optical read-only disks and the common disk player is designed specifically for this type of disk. These disks have a reflective surface containing pits which represent data in binary form. The pits are arranged in a spiral pattern with a 1.6 .mu.m pitch and define both informational data, e.g., music or text, and control data which provide instructions to the player on how to play the disk. Specific control information includes start-of-disk codes, end-of-disk codes, tracking information, rotational speed information, and the like. A detailed description of these pits and how they function is provided by Watkinson, The Art of Digital Audio, Focal Press, Chapter 13.
Compact disks are currently produced by a pressing process similar to the process used to produce conventional long playing records. The process, referred to herein as the "mastering" process, starts by first polishing a plain glass optical disk. This disk has an outside diameter from 200 to 240 mm, a thickness of 6 mm and undergoes various cleaning and washing steps. The disk is then coated with a thin chrome film or coupling agent, a step taken to produce adhesion between the glass disk and a layer of photo-resist, which is a photosensitive material. Data on a compact disk master tape are then transferred to the glass disk by a laser beam cutting method.
The glass disk is still completely flat after it is written on by the laser beam because pits are not formed until the glass is photographically developed. The disk surface is first made electrically conductive and then subjected to a nickel evaporation process. The disk, now known as the glass master, then undergoes nickel electrocasting, a process which is similar to that used in making analog phono records. A series of metal replications follow, resulting in a disk called a stamper. The stamper is equivalent to a photographic negative in the sense that it is a reverse of the final compact disk; that is, there are now bumps were there should be pits. This stamper is then used to make a pressing on a transparent polymer such as polyvinyl chloride, poly(ethyl-methacrylate) and polycarbonate. The stamped surface is then plated with a reflective film such as aluminum or other metal and finally a plastic coating is applied over the film to form a rigid structure.
The player operates by focusing a laser beam on the reflective metal through the substrate and then detecting reflected light. The optical properties of the substrate, such as its thickness and index of refraction, are thus critical to the player's detection systems and standard players are designed specifically with these parameters in mind.
The pits increase the optical path of the laser beam by an amount equivalent to a half wavelength, thereby producing destructive interference when combined with other (non-shifted) reflected beams. The presence of data thus takes the form of a drop in intensity of the reflected light. The detection system on a standard player is thus designed to require greater than 70% reflection when no destructive interference occurs and a modulation amplitude greater than 30% when data is present. These intensity limits, combined with the focusing parameters, set the criteria for the compact disks and other optical data storage media which can be read or played on such players. U.S. Pat. No. 4,432,083 describes a system for reading and tracking information on optical disks.
Media on which data can be recorded directly on and read directly from have a different configuration and operate under a somewhat different principle. One example is described in U.S. Pat. No. 4,719,615 (Feyrer et. al.), the disclosure of which is incorporated herein by reference. Other examples are described in copending application serial numbers 152,690; 294,723; 357,377; 357,504; 357,506; 414,041; and 414,044, the disclosures of Which are incorporated herein by reference.
The medium disclosed in Feyrer et. al, includes a lower expansion layer of a rubbery material which expands when heated. The expansion layer is coupled to an upper retention layer which is glassy at ambient temperature and becomes rubbery when heated. Both layers are supported on a rigid substrate. The expansion and retention layers each contain dyes for absorption of light at different wavelengths. Data are recorded by heating the expansion layer by absorption of light from a laser beam at a "record" wavelength to cause the expansion layer to expand away from the substrate and form a protrusion or "bump" extending into the retention layer. While this is occurring, the retention layer rises in temperature above its glass transition temperature so that it can deform to accommodate the bump. The beam is then turned off and the retention layer cools quickly to its glassy state before the bump levels out, thereby fixing the bump. Reading or playback of the data is then achieved by a low intensity "read" beam which is focused on the partially reflecting interface between the retention layer and air. When the read beam encounters the bump, some of the reflected light is scattered, while other portions of the reflected light destructively interfere with reflected light from non-bump areas. The resulting drop in intensity is registered by the detector. Removal of the bump to erase the data is achieved by a second laser beam at an "erase" wavelength which is absorbed by the retention layer and not the expansion layer. This beam heats the retention layer alone to a rubbery state where its viscoelastic forces and those of the expansion layer return it to its original flat configuration. The write, read and erase beams all enter the medium on the retention layer side, passing through retention layer before reaching the expansion layer.
In recording data on blank recordable disks, it is necessary to both rotate the disk and translate the recording laser beam across the disk in a coordinated fashion in order to impart data on the disk in a readable format. Usually, the data will be recorded in a spiral pattern on the disk and it is necessary to provide tracking pattern and rotational speed control information to the recorder in order to properly coordinate the position of the laser beam and the rotational position of the disk. In addition, information must be provided to facilitate playback of the disk, including start-of-disk codes, end-of-disk codes, rotational speed codes, and the like. When the recorded disks are intended to be played back on conventional disk players, it is necessary that all encoded tracking speed, and other control information be compatible with the particular standardized system.
One approach for providing tracking, speed, and other control information on recordable disk media has been to incorporate the information on the blank during the manufacturing process. For example, digital data comprising the start-of-disk codes, end-of-disk codes, and rotational speed information can be pressed into the "blank" disk in a manner similar to conventional disk fabrication, while a spiral track or groove can be formed into the disk to allow tracking of the recording laser during the recording process. The need to incorporate such information at the manufacturing stage, however, is problematic and significantly increases the cost complexity of fabricating the disks. Moreover, the tracking grooves must be invisible to conventional disk players, further complicating their design and manufacture.
For these reasons, it would be desirable to provide methods and systems for encoding format information on blank recordable media during the recording process. In particular, it would be desirable to impart both tracking information and digital control information, such as start-of-disk codes, end-of-disk codes, and rotational speed codes, during the recording process.